1. Field of the Invention
The present invention generally relates to a communication system. More particularly, the present invention relates to an apparatus and method for connecting a call.
2. Description of the Related Art
In the present communication systems, a terminal, for example, a wired one or a wireless one attempts to connect a call to communicate with another terminal. For the call connection, the terminal transmits a call connection request message to an exchange that manages calls for the terminal, to thereby communicate with the other terminal.
Conventionally, when a first terminal attempts to connect a call to a busy second terminal, the second terminal can be notified of the call connection request. This is called “call waiting service”. The call waiting service enables the first terminal to communicate with the second terminal by the notification of the call connection request from the first terminal, even when the second terminal is busy.
However, if a terminal requests a call connection to a second terminal that is requesting a call connection to a third terminal or is receiving a call connection request from the third terminal, it receives a busy message indicating that the second terminal is busy. Especially when a communication service is suddenly discontinued during a conversation between terminals, they request a call connection to each other. Consequently, even though a call connection is in progress for them, that is, they are in a call connecting state, they just receive busy messages. An operation of terminals in the call connecting state will be described below.
FIG. 1 is a diagram illustrating a signal flow when terminals request a call connection to each other simultaneously in a conventional communication system.
Referring to FIG. 1, the communication system includes an exchange 110, a first terminal 120 (terminal 1), and a second terminal 130 (terminal 2).
The exchange 110 can be incorporated into or connected to a Base Station (BS), a Base Station Controller (BSC), or the like, if the terminals 120 and 130 are wireless terminals. The exchange 110 provides a communication service to terminals by operations including call connection and call release in the communication system.
When terminal 1 determines to connect a call to terminal 2, it transmits a call connection request message requesting a call connection to terminal 2 to the exchange 110 in step 111.
When terminal 2 also determines to connect a call to terminal 1, it transmits a call connection request message requesting a call connection to terminal 1 to the exchange 110 in step 113.
The exchange 110 transmits a call connection attempt message to terminal 2 in response to the call connection request of terminal 1 in step 115.
Since terminal 2 is also requesting the call connection to terminal 1, the call connection between them is impossible. Hence, terminal 2 transmits a busy message to the exchange 110 in step 117.
In step 119, the exchange 110 transmits a call connection attempt message to terminal 1 in response to the call connection request of terminal 2.
Since terminal 1 is also requesting the call connection to terminal 2, the call connection between them is impossible. Hence, terminal 1 transmits a busy message to the exchange 110 in step 121.
The exchange 110 transmits a message indicating that terminal 2 is busy to terminal 1 in step 123.
Also, the exchange 110 transmits a message indicating that terminal 1 is busy to terminal 2 in step 125.
As described above, when terminals request a call to each other simultaneously, they receive wrong state information indicating that the other party is busy although the other party is not.
FIG. 2 is a diagram illustrating a signal flow when a terminal receives another call connection request from a second terminal during receiving a call connection request from a third terminal in the conventional communication system.
Referring to FIG. 2, the communication system includes an exchange 210, a first terminal 220 (terminal 1), a second terminal 230 (terminal 2), and a third terminal 240 (terminal 3).
The exchange 210 can be incorporated into or connected to a BS, a BSC, or the like, if the terminals 220, 230 and 240 are wireless ones. The exchange 210 provides a communication service to terminals by operations including call connection and call release in the communication system.
When terminal 3 determines to connect a call to terminal 1, it transmits a call connection request message requesting a call connection to terminal 1 to the exchange 210 in step 211.
When terminal 2 also determines to connect a call to terminal 1, it transmits a call connection request message requesting a call connection to terminal 1 to the exchange 210 in step 213.
The exchange 210 transmits a call connection attempt message to terminal 1 in response to the call connection request of terminal 3 in step 215.
The exchange 210 also transmits a call connection attempt message to terminal 1 in response to the call connection request of terminal 2 in step 217.
However, since terminal 1 is receiving the call connection request from terminal 3, the call connection between terminal 1 and terminal 2 is impossible. Hence, terminal 1 transmits a busy message to the exchange 210 in step 219.
The exchange 210 transmits a message indicating that terminal 1 is busy to terminal 2 in step 220.
As described above, when a terminal (e.g. terminal 1) receives another call connection request from terminal 2, for example, during receiving a call connection request, terminal 2 receives wrong state information indicating that terminal 1 is busy although it is not.
FIG. 3 is a diagram illustrating a signal flow when a terminal receives a call connection request from a second terminal during requesting a call connection to a third terminal in the conventional communication system.
Referring to FIG. 3, the communication system includes an exchange 310, a first terminal 320 (terminal 1), a second terminal 330 (terminal 2), and a third terminal 340 (terminal 3).
The exchange 310 can be incorporated into or connected to a BS, a BSC, or the like, if the terminals 320, 330 and 340 are wireless terminals. The exchange 310 provides a communication service to terminals by operations including call connection and call release in the communication system.
When terminal 1 determines to connect a call to terminal 3, it transmits a call connection request message requesting a call connection to terminal 3 to the exchange 310 in step 311.
When terminal 2 also determines to connect a call to terminal 1, it transmits a call connection request message requesting a call connection to terminal 1 to the exchange 310 in step 313.
The exchange 310 transmits a call connection attempt message to terminal 3 in response to the call connection request of terminal 1 in step 315.
The exchange 310 also transmits a call connection attempt message to terminal 1 in response to the call connection request of terminal 2 in step 317.
However, since terminal 1 is requesting the call connection request to terminal 3, the call connection between terminal 1 and terminal 2 is impossible. Hence, terminal 1 transmits a busy message to the exchange 310 in step 319.
The exchange 310 transmits a message indicating that terminal 1 is busy to terminal 2 in step 321.
As described above, when terminal 1 requests a call connection to terminal 3 during receiving a call connection request from terminal 2, terminal 2 receives wrong state information indicating that terminal 1 is busy although it is not.
In this manner, although a call connection is in progress between first and second terminals, the exchange transmits wrong information indicating that the other party is busy to each of the terminals. When a third terminal requests a call connection to one of the first and second terminals that are placed in the call connecting state, the exchange also transmits to the third terminal wrong information indicating that the first or second terminal is busy.
Especially, when an on-going call is interrupted in a wireless communication system, terminals can request a call connection to each other at the same time. In this case, the terminals have no way in finding out that the call connection is in progress, simply determining that the other party is busy.